Novolak resin blends for photoresist applications

Abstract

The present invention relates to a water insoluble, aqueous alkali soluble novolak resin blend, wherein the resin blend comprises two novolaks having dissimilar relative molecular weights and similar dissolution rates, a process for producing such a resin blend, a photoresist containing such a resin blend and a method for producing a semi-conductor device utilizing such a photoresist.

We claim: 
     
       1. A positive photoresist composition comprises an admixture of: a) a photosensitive component in an amount sufficient to uniformly photosensitize the photoresist composition; and   b) a water insoluble, aqueous alkali soluble novolak resin blend "wherein the lithographic performance, L, equals RMW a  -RMW b  and L is greater than or equal to 2.0, " comprising providing a mixture of two novolak resins, with the same or different chemical composition, relative molecular weights (RMW) that differ by more than about 5% and dissolution rates DR that differ by less than 2.0; and   c) a suitable solvent.   
     
     
       2. The photoresist composition of claim 1 wherein the relative molecular weights of the two novolak resins differ by more than about 10%. 
     
     
       3. The photoresist composition of claim 1 wherein the relative molecular weights of the two novolak resins differ from about 10% to about 60%. 
     
     
       4. The photoresist composition of claim 1 wherein the relative molecular weights of the two novolak resins differ from about 25% to about 50%. 
     
     
       5. The photoresist composition of claim 1 wherein the dissolution rates of the two novolak resins differ by less than about 1.5. 
     
     
       6. The photoresist composition of claim 1 wherein the dissolution rates of the two novolak resins differ by less than about 1.0. 
     
     
       7. The photoresist composition of claim 1 wherein the dissolution rates of two novolak resins differ by less than about 0.5. 
     
     
       8. The photoresist composition of claim 1 wherein L is greater than or equal to 4.0. 
     
     
       9. The photoresist composition of claim 1 wherein L is greater than or equal to 6.0. 
     
     
       10. The photoresist composition of claim 1 wherein L is greater than or equal to 8.0. 
     
     
       11. The photoresist composition of claim 1 wherein said photosensitive component is an ester of an alcoholic or phenolic residue and a sulfonic acid or sulfonic acid derivative. 
     
     
       12. The photoresist composition of claim 1 wherein said solvent is selected from the group consisting of propylene glycol mono-alkyl ether, propylene glycol alkyl ether acetate, butyl acetate, xylene, ethylene glycol monoethyl ether acetate, ethyl lactate, ethyl-3-ethoxypropionate, and mixtures of ethyl lactate and ethyl-3-ethoxypropionate. 
     
     
       13. The photoresist composition of claim 1 wherein said solvent is propylene glycol monomethyl ether acetate. 
     
     
       14. A method for producing a semiconductor device by producing a photoresist image on a substrate by coating a suitable substrate with a positive working photoresist composition which composition comprises an admixture of: a) a photosensitive component in an amount sufficient to photosensitize the photoresist composition; and   b) a water insoluble, aqueous alkali soluble novolak resin blend comprising a mixture of two novolak resins, having the same or different chemical composition, relative molecular weights that differ by more than 5% and dissolution rates that differ by less than 2.0; and   c) a suitable solvent; and   d) heat treating the coated substrate until substantially all of the solvent is removed; image-wise exposing the photosensitive composition; and removing the image-wise exposed areas of such composition with an aqueous alkaline developer.   
     
     
       15. The photoresist composition of claim 14 wherein the lithographic performance, L, equals RMW a  -RMW b  /DR a  -DR b  and L is greater than or equal to 2.0. 
     
     
       16. The process of claim 14 wherein the relative molecular weights of the two novolak resins differ by more than about 10%. 
     
     
       17. The process of claim 14 wherein the relative molecular weights of the two novolak resins differ from about 10% to about 60%. 
     
     
       18. The process of claim 14 wherein the relative molecular weights of the two novolak resins differ from about 25% to about 50%. 
     
     
       19. The process of claim 14 wherein the dissolution rates of the two novolak resins differ by less than about 1.5. 
     
     
       20. The process of claim 14 wherein the dissolution rates of the two novolak resins differ by less than about 1.0. 
     
     
       21. The process of claim 14 wherein the dissolution rates of two novolak resins differ by less than about 0.5. 
     
     
       22. The process of claim 15 wherein L is greater than or equal to 4.0. 
     
     
       23. The process of claim 15 wherein L is greater than or equal to 6.0. 
     
     
       24. The process of claim 15 wherein L is greater than or equal to 8.0. 
     
     
       25. The method of claim 14 wherein said photosensitive component is an ester of an alcoholic or phenolic residue and a sulfonic acid or sulfonic acid derivative. 
     
     
       26. The method of claim 14 wherein said solvent is selected from the group consisting of propylene glycol mono-alkyl ether, propylene glycol alkyl ether acetate, butyl acetate, xylene, ethylene glycol monoethyl ether acetate, ethyl lactate, ethyl-3-ethoxypropionate, and mixtures of ethyl lactate and ethyl-3-ethoxypropionate. 
     
     
       27. The method of claim 14 wherein said solvent is propylene glycol monomethyl ether acetate.